Improvement of reverse recovery using oxygen-vacancy defects

ABSTRACT

A semiconductor device comprises a semiconductor substrate, a first electrode formed on a first main surface of the semiconductor substrate, and a second electrode formed on a second main surface of the semiconductor substrate. The semiconductor substrate includes a first region in which a density of oxygen-vacancy defects is greater than a density of vacancy cluster defects, and a second region in which the density of vacancy cluster defects is greater than the density of oxygen-vacancy defects.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2009-285078 filed on Dec. 16, 2009 and Japanese Patent Application No.2010-169360 filed on Jul. 28, 2010, the contents of which are herebyincorporated by reference into the present application.

TECHNICAL FIELD

The present invention relates to a semiconductor device. The presentinvention, in particular, relates to a free wheel diode which isconnected to a power semiconductor device in an inverse-parallelconnection.

DESCRIPTION OF RELATED ART

A diode is used in many types of electrical circuits, and its functioncovers widespread fields. For example, the diode is used in an invertercircuit which controls a supply of an electrical power to a load. Theinverter circuit comprises a plurality of power semiconductor devicesbeing in bride connection, and diodes are connected to these powersemiconductor devices in an inverse-parallel connection respectively.This type of diode is referred to as a Free Wheel Diode (hereinafterreferred to as “FWD”). The FWD communicates a load current when thepower semiconductor device performs an on-off control of the loadcurrent.

In recent years, the inverter circuit for controlling a motor disposedin a hybrid car or an electric car is required to have a low switchingloss and a high surge breakdown voltage. In order to meet theserequirements, a reverse recovery property of the FWD needs to beimproved. In particular, efforts of lowering of a reverse recoverycharge (Qrr) for the low switching loss and softening of a recoverycurrent which contributes in the high surge breakdown voltage have beenmade by forming crystal defects within the semiconductor substrate.

WO 99/09600 A, JP H06-35010 A and JP 2004-88012 A disclose a techniquefor improving the reverse recovery property of the FWD. In theaforementioned prior art, the reverse recovery property of the FWD isimproved by combining two types of crystal defects within thesemiconductor substrate: one type of crystal defects is formed by usinga diffusion of a heavy metal, and another type of crystal defects isformed by using an irradiation of charged particles.

SUMMARY

In general, an energy level of the crystal defects is a recombinationcenter for electrons and holes, and also a generation center forelectrons and holes when a high electrical field is applied (a reversebiased state). Therefore, if many crystal defects are formed within thesemiconductor substrate, an increase of leak current may occur under thereverse biased state. It is known that crystal defects formed by usingthe diffusion of the heavy metal have a low generation degree ofelectrons and holes (the generation degree of electrons and holeshereinafter referred to as “a generation probability”). Therefore, theleak current is repressed in the case where the type of crystal defectsformed within the semiconductor substrate is originated from thediffusion of the heavy metal. However, the crystal defects formed byusing the diffusion of the heavy metal has a problem that arecombination degree of electrons and holes (hereinafter referred to as“a recombination probability”) easily varies based on a temperature. Onthe other hand, the crystal defects formed by using the irradiation ofcharged particles is characterized in that the recombination probabilityof electrons and holes does not vary based on the temperature. In theabove mentioned prior art, both types of crystal defects formed by usingthe diffusion of the heavy metal and irradiation of the charged particleare combined within the semiconductor substrate, therefore, it resultsin the lowering of the reverse recovery charge (Qrr) and the softeningof the recovery current while repressing the increase of the leakcurrent.

However, in the above mentioned prior art, the crystal defects areformed by using the heavy metal (e.g. platinum). The process for dopingthe heavy metal into the semiconductor substrate needs specialequipments for preventing a pollution of the heavy metal. Such specialequipments are different from general semiconductor manufacturingequipments. Therefore, a use of the heavy metal severely raises a costof a manufacturing of the semiconductor device.

The technique disclosed in the present specification may provide asemiconductor device in which different types of crystal defects arecombined without the use of the heavy metal.

Inventors of the present teachings focused on the energy level of thecrystal defects. The crystal defects formed by using the diffusion ofthe heavy metal have the energy level of the recombination center at alevel 0.23 eV lower from a conductance band energy edge (Ec). On theother hand, the crystal defects formed by using the irradiation ofcharged particles are vacancy cluster defects which a plurality ofatomic vacancies is combined, and have the energy level of therecombination center at 0.40 eV lower from the conductance band energyedge (Ec). In comparison, crystal defects formed by using the diffusionof the heavy metal have a shallow energy level, and crystal defectsformed by using the irradiation of charged particles have a deep energylevel.

As a result of a research by the inventors of the present teachings, itwas found that the recombination probability and the generationprobability of electrons and holes depend on the energy level of crystaldefects. FIG. 1 shows a relationship between the energy level of crystaldefects and the recombination probability in the case of a single trap,and also shows a relationship between the energy level of crystaldefects and the generation probability in the case of the single trap.As shown in FIG. 1, the generation probability of electrons and holes atthe shallow energy level of crystal defects (e.g. crystal defects formedby using the diffusion of the heavy metal) is low, therefore, the leakcurrent can be repressed. However, the recombination probability ofelectrons and holes at the shallow energy level of crystal defectsvaries based on the temperature. On the other hand, the recombinationprobability of electrons and holes at the deep energy level of crystaldefects (e.g. the crystal defects formed by using the irradiation ofcharged particles) does not vary based on the temperature. Hence, itcomes to appear that the recombination probability and the generationprobability of electrons and holes depend on the energy level of crystaldefects. Therefore, it is expected that the semiconductor device inwhich different types of crystal defects are combined without the use ofthe heavy metal may be realized if crystal defects having the energylevel as shallow as crystal defects formed by using the heavy metal areformed.

A semiconductor device disclosed in the present specification maycomprise a semiconductor substrate, a first electrode formed on a firstmain surface of the semiconductor substrate, and a second electrodeformed on a second main surface of the semiconductor substrate. Thesemiconductor substrate may include a first region in which a density ofoxygen-vacancy defects is greater than a density of vacancy clusterdefects, and a second region in which the density of vacancy clusterdefects is greater than the density of oxygen-vacancy defects. Thesemiconductor device disclosed in the present specification ischaracterized in that oxygen-vacancy defects are formed therein. Theoxygen-vacancy defects have the energy level at about 0.17 eV lower fromthe conductance band energy edge (Ec), and its energy level is almostidentical with the energy level of crystal defects formed by using thediffusion of the heavy metal. Therefore, oxygen-vacancy defects mayalter crystal defects formed by using the diffusion of the heavy metal.If oxygen-vacancy defects are formed, a semiconductor device in whichdifferent types of crystal defects are combined is realized without theuse of the heavy metal.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a relationship between an energy level of crystal defectsand a recombination probability, and also shows a relationship betweenthe energy level of crystal defects and a generation probability ofelectrons and holes.

FIG. 2 shows a schematic cross sectional view of an essential part of adiode in an embodiment.

FIG. 3 shows a schematic overview of a manufacturing method of the diodein the embodiment.

FIG. 4 shows a first step of the manufacturing method of the diode inthe embodiment.

FIG. 5 shows a second step of the manufacturing method of the diode inthe embodiment.

FIG. 6 shows a calculated value of an oxygen density introduced withinan epitaxial layer.

FIG. 7 shows a measured value of the oxygen density introduced withinthe epitaxial layer.

FIG. 8 shows a third step of the manufacturing method of the diode inthe embodiment.

FIG. 9 shows a forth step of the manufacturing method of the diode inthe embodiment.

FIG. 10 shows a fifth step of the manufacturing method of the diode inthe embodiment.

FIG. 11 shows a sixth step of the manufacturing method of the diode inthe embodiment.

FIG. 12 shows a seventh step of the manufacturing method of the diode inthe embodiment.

FIG. 13 shows distributions of an impurity density and a crystal defectdensity of the diode in the embodiment.

FIG. 14 shows distributions of an impurity density and a crystal defectdensity of the diode in one modified embodiment.

FIG. 15 shows distributions of an impurity density and a crystal defectdensity of the diode in another modified embodiment.

DETAILED DESCRIPTION OF INVENTION

FIG. 2 shows a schematic cross sectional view of a diode 10. Note thatFIG. 2 only depicts an element region and does not depict a terminalregion disposed around the element region. The diode 10 comprises asemiconductor substrate 20 of monocrystal silicon, a cathode electrode30 formed on a first main surface 20 a of the semiconductor substrate 20and an anode electrode 70 formed on a second main surface 20 b of thesemiconductor substrate 20. The diode 10 belongs to a so-called verticaltype PIN diode.

As shown in FIG. 2, the semiconductor substrate 20 comprises a cathoderegion 42, an electrical field inhibition region 44 formed on thecathode region 42, a voltage maintaining region 50 formed on theelectrical field inhibition region 44 and an anode region 60 formed onthe voltage maintaining region 50. The cathode region 42 and theelectrical field inhibition region 44 include a higher density of n-typeimpurities than the voltage maintaining region 50. The cathode region 42and the electrical field inhibition region 44 may be referred to as ann-type impurity introducing region 40. The cathode region 42 is incontact with the cathode electrode 30. The voltage maintaining region 50isolates the n-type impurity introducing region 40 and the anode region60. The voltage maintaining region 50 includes a lower density of n-typeimpurities. The anode region 60 includes a higher density of p-typeimpurities and be in contact with the anode electrode 70.

Next, a manufacturing method of the diode 10 will be explained referringto a flow shown in FIG. 3. First, as shown in FIG. 4, an n-type basesubstrate 140 (which later becomes the n-type impurity introducingregion 40) is prepared. In one embodiment, the impurity density of thebase substrate 140 is about 1×10¹⁵ cm⁻³. Next, an n⁻-type epitaxiallayer 150 (which later becomes the voltage maintaining region 50 and theanode region 60) is grown on the base substrate 140 by using thetechnique of the epitaxial growth. In one embodiment, the thickness ofthe epitaxial layer 150 is about 100 μm and its impurity density isabout 1×10¹⁴cm³.

Next, as shown in FIG. 5, a silicon oxide film 52 is formed on theepitaxial layer 150 under an oxygen atmosphere by using the technique ofthe thermal oxidation. In this thermal oxidation step, it is preferablethat an atmosphere temperature is set between 1100-1200 degrees Celsius(° C.), and a thermal oxidation time is set between 10-500 minutes. Inthis thermal oxidation step with the above condition, oxygen isintroduced into a surface portion of the epitaxial layer 150 up to itssolid solubility limit concentration. Next, oxygen introduced into thesurface portion of the epitaxial layer 150 are diffused toward a deepportion of the epitaxial layer 150 under an inert gas atmosphere byusing the technique of the heat treatment. In this heat treatment step,it is preferable that an atmosphere temperature is set more than 1150degrees Celsius. In this heat treatment step with the above condition,oxygen can be diffused to a deeper location at least than a rangelocation of helium in a helium irradiation step which will be describedhereinafter. Specifically, it is preferable that a target value of anoxygen density introduced within the epitaxial layer 150 is more than1×10¹⁷ cm⁻³ at 10 μm depth, more preferable more than 1×10¹⁷ cm⁻³ at 20μm depth.

FIG. 6 shows a calculated value of the oxygen density introduced withinthe epitaxial layer 150 by the thermal oxidation step and the heattreatment step. The FIG. 7 shows a measured value of the oxygen densityintroduced within the epitaxial layer 150 by the thermal oxidation stepand the heat treatment step. A vertical axis indicates the oxygendensity and a horizontal axis indicates a depth from the surface of theepitaxial layer 150.

In FIG. 6, calculated values 1 and 2 show expected results in the casewhere only the thermal oxidation step is performed. In the thermaloxidation step of the calculated value 1, the atmosphere temperature isset at 1100 degrees Celsius and the thermal oxidation time is set at 49minutes. In the thermal oxidation step of the calculated value 2, theatmosphere temperature is set at 1200 degrees Celsius and the thermaloxidation time is set at 10 minutes. Calculated values 3 to 5 showexpected results in the case where both of the thermal oxidation stepand the heat treatment step are performed. In the thermal oxidation stepof the calculated value 3, the atmosphere temperature is set at 1100degrees Celsius and the thermal oxidation time is set at 49 minutes. Inthe thermal oxidation step of the calculated value 4, the atmospheretemperature is set at 1150 degrees Celsius and the thermal oxidationtime is set at 180 minutes. In the thermal oxidation step of thecalculated value 5, the atmosphere temperature is set at 1150 degreesCelsius and the thermal oxidation time is set at 440 minutes. In theheat treatment step of calculated values 3 to 5, the atmospheretemperature is set at 1150 degrees Celsius and the heat treatment timeis set at 328 minutes.

As shown in FIG. 6, all calculated values 1 to 5 indicate that theoxygen can be introduced within the epitaxial layer 150 over the targetvalue. In particular, the calculated values 3 to 5 for which both of thethermal oxidation step and the heat treatment step were performedindicate that oxygen can be introduced over the target value even at adeeper portion of the epitaxial layer 150. Comparing the calculatedvalue 1 with the calculated value 2, it indicates that the oxygendensities respectively introduced by the thermal oxidation step arealmost the same therebetween.

Next, the calculated values of FIG. 6 are verified by the measuredvalues of FIG. 7. In FIG. 7, measured values 11 and 12 show results inthe case where only the thermal oxidation step is performed. In thethermal oxidation step of the measured value 11, the atmospheretemperature is set at 1100 degrees Celsius and the thermal oxidationtime is set at 49 minutes. In the thermal oxidation step of the measuredvalue 12, the atmosphere temperature is set at 1150 degrees Celsius andthe thermal oxidation time is set at 49 minutes. Measured values 13 to15 show results in the case where both of the thermal oxidation step andthe heat treatment step are performed. In the thermal oxidation step ofthe measured value 13, the atmosphere temperature is set at 1100 degreesCelsius and the thermal oxidation time is set at 49 minutes. In thethermal oxidation step of the measured value 14, the atmospheretemperature is set at 1150 degrees Celsius and the thermal oxidationtime is set at 180 minutes. In the thermal oxidation step of themeasured value 15, the atmosphere temperature is set at 1150 degreesCelsius and the thermal oxidation time is set at 440 minutes. In theheat treatment step of measured values 13 to 15, the atmospheretemperature is set at 1150 degrees Celsius and the heat treatment timeis set at 328 minutes (nitrogen is used as an inert gas). Further, inFIG. 7, some examples which the thermal oxidation time in the thermaloxidation step is longer are verified for the reference. Measured values16 and 17 show results in the case where only the thermal oxidation stepwith the longer thermal oxidation time is performed. In the thermaloxidation step of the measured value 16, the atmosphere temperature isset at 1150 degrees Celsius and the thermal oxidation time is set at 440minutes. In the thermal oxidation step of the measured value 17, theatmosphere temperature is set at 1150 degrees Celsius and the thermaloxidation time is set at 615 minutes.

In the thermal oxidation step of the measured values 11 to 14, apyrogenic oxidation with oxide gas and hydrogen gas is used. In thethermal oxidation step of the measured values 15 and 16, a dry oxidationwith oxide gas and hydrogen gas is used. In the thermal oxidation stepof the measured value 17, a nitrogen dilution dry oxidation with oxidegas and diluted nitrogen gas is used. The oxygen density of the siliconoxide film 52 will differ based on the difference of these oxidationmethods. However, since every oxygen densities of the silicon oxidefilms 52 are higher than the solid solubility limit of the epitaxiallayer 150, it is supposed that difference of these oxidation methodsdoes not affect the oxygen density introduced within the epitaxial layer150.

As shown in FIG. 7, it is verified that these results are almost thesame as the expected calculated values in FIG. 6. It is verified thatthe method for performing the thermal oxidation step and the heattreatment step are useful in introducing oxygen with higher density intothe epitaxial layer 150. Further, in comparing the measured values 13 to15 with the measured values 11, 12, 16 and 17, it is verified that themethod for combining the thermal oxidation step and the heat treatmentstep can help to introduce oxygen such that the gradient of the oxygendensity along the thickness direction is gradual and oxygen can beintroduced to deeper portion.

Although conditions in the above the thermal oxidation step and the heattreatment step are not limited to above-mentioned conditions, it ispreferable that the oxygen density of an entire areas in the epitaxiallayer 150 and the base substrate 140 in the thickness direction risesafter the thermal oxidation step and the heat treatment step. It is morepreferable that oxygen distributes such that the oxygen density isconstant within the epitaxial layer 150 and the base substrate 140 afterthe thermal oxidation step and the heat treatment step. As mentionedabove, when oxygen is introduced from the silicon oxide film 52, a peakof the oxygen density does not appear within the epitaxial layer 150 andthe base substrate 140. In one embodiment, it is preferable that theoxygen density within the epitaxial layer 150 and the base substrate 140is adjusted between 1×10¹⁷ cm⁻³ and 3×10¹⁷ cm⁻³. Note that, in oneembodiment, oxygen ions may be introduced within the epitaxial layer 150and the base substrate 140 by using the ion irradiation technique beforethe heat treatment step.

Next, as shown in FIG. 8, the silicon oxide film 52 on the elementregion is removed by using the techniques of the photoresist and theetching. Next, boron is introduced within the surface portion of theepitaxial layer 150 by using the technique of the ion implantation.After the implantation of boron, introduced boron is activated by usingthe technique of the thermal diffusion so that the anode region 60 isformed. As a result of the ion implantation step and the thermaldiffusion step, a left region of the epitaxial layer 150 other than theanode region 60 becomes the voltage maintaining region 50. In oneembodiment, the peak density of impurities in the anode region 60 isabout 1×10¹⁷ cm⁻³, and the thickness of the anode region 60 is about 2μm.

Next, as shown in FIG. 9, the anode electrode 70 is foamed on the anoderegion 60 by using the techniques of the vapor deposition and thesputtering. In one embodiment, the material of the anode electrode 70 isaluminum.

Next, as shown in FIG. 10, the base substrate 140 is polished to be apredetermined thickness so that the n-type impurity introducing region40 is formed. In one embodiment, the thickness of the n-type impurityintroducing region 40 is about 30 μm.

Next, as shown in FIG. 11, phosphorus is introduced within a bottomportion of the base substrate 140 by using the technique of the ionimplantation. After the implantation of phosphorus, phosphorus areactivated by using the technique of the laser anneal so that the cathoderegion 42 is formed. As a result of the ion implantation step and thelaser anneal step, a left region of the n-type impurity introducingregion 40 other than the cathode region 42 become the electrical fieldinhibition region 44. In one embodiment, the peak density of impuritiesin the cathode region 42 is about 1×10²⁰ cm⁻³, and the thickness of thecathode region 42 is about 0.2 μm.

Next, as shown in FIG. 12, helium of mass “3” is irradiated from then-type impurity introducing region 40 side by using the technique of thehelium irradiation. The range location is set at the voltage maintainingregion 50 side adjacent to a pn joint interface between the voltagemaintaining region 50 and the anode region 60. The range location isadjusted based on a thickness of undepicted aluminum foil for energyabsorption. Next, oxygen-vacancy defects and vacancy cluster defects areformed by performing the postdeposition annealing. Finally, the cathodeelectrode 30 is formed by using the technique of the vapor depositionand the sputtering. In one embodiment, the material of the cathodeelectrode 30 is aluminum. The diode 10 shown in FIG. 2 is manufacturedthrough these steps.

The FIG. 13 shows distributions of the impurity density and the crystaldefect density. The broken line 80 shows the density of vacancy clusterdefects formed by the irradiation of helium. The broken line 90 showsthe density of oxygen-vacancy defects formed by combining the introducedoxygen with the vacancy. The diode 10 comprises a first region 90A inwhich the density of oxygen-vacancy defects 90 is greater than thedensity of vacancy cluster defects 80, and a second region 80A in whichthe density of vacancy cluster defects 80 is greater than the density ofoxygen-vacancy defects 90. The first region 90A is located at the n-typeimpurity introducing region 40 and at the part of the voltagemaintaining region 50 where is the n-type impurity introducing region 40side. The second region 80A is located at the anode region 60 and at thepart of the voltage maintaining region 50 where is the anode region 60side. Further, as shown in FIG. 13, the first region 90A is a regionwhere the oxygen-vacancy defects 90 are formed such that the introducedoxygen combines with the vacancy, and also a region where the vacancycluster defects 80 are formed by the irradiation of helium. Althoughboth of the oxygen-vacancy defects 90 and the vacancy cluster defects 80are formed, the first region 90A is a region where the density ofoxygen-vacancy defects 90 is greater than the density of vacancy clusterdefects 80. On the other hand, the second region 80A is a region wherethe vacancy cluster defects 80 are formed by the irradiation of helium,and also a region where the oxygen-vacancy defects 90 are formed suchthat the introduced oxygen combines with the vacancy. Although both ofthe vacancy cluster defects 80 and the oxygen-vacancy defects 90 areformed, the second region 80A is a region where the density of vacancycluster defects 80 is greater than the density of oxygen-vacancy defects90.

The oxygen-vacancy defects 90 have the energy level at 0.17 eV lowerfrom the conductance band energy edge (Ec), and its energy level belongsto a shallow energy level. Hence, as shown in FIG. 1, the generationprobability of electrons and holes in the oxygen-vacancy defects 90 islow. Therefore, even if the oxygen-vacancy defects 90 are formed in hugeamount, the leak current can be repressed. In particular, theoxygen-vacancy defects 90 are formed all over the semiconductorsubstrate 20 in the diode 10. As a result, the reverse recovery charge(Qrr) is drastically repressed while the leak current is repressed.However, the recombination probability of electrons and holes in theoxygen-vacancy defects 90 vary based on the temperature. In the diode10, the vacancy cluster defects 80 formed by the irradiation of heliumare formed at the pn joint interface between the voltage maintainingregion 50 and the anode region 60. The vacancy cluster defects 80 havethe energy level that is lower by 0.40 eV from the conductance bandenergy edge (Ec), and its energy level belongs to a deep energy level.Hence, the recombination probability of vacancy cluster defects 80 ischaracterized in that it does not vary based on the temperature. In thediode 10, the vacancy cluster defects 80 can compensate a temperaturedependence of the recombination probability of electrons and holes inthe oxygen-vacancy defects 90. Further, in the diode 10, since the peakvalue of the vacancy cluster defects 80 is formed at the pn jointinterface between the voltage maintaining region 50 and the anode region60, the recovery current can be softened. As mentioned above, in thediode 10, the oxygen-vacancy defects 90 as the shallow energy level andthe vacancy cluster defects 80 as the deep energy level are mixed sothat the lowering of the reverse recovery charge (Qrr) and softening ofthe recovery current are realized while the increasing of the leakcurrent is repressed.

FIG. 14 shows distributions of the impurity density and the crystaldefect density in one modified embodiment. In the diode of the modifiedembodiment, it is characterized in that the vacancy cluster defects 80formed by the irradiation of helium are formed in a narrow range. Inparticular, the vacancy cluster defects 80 are not formed at the pnjoint interface between the voltage maintaining region 50 and the anoderegion 60, but are formed within the voltage maintaining region 50. Inone embodiment, this modified diode can be formed such that the heliumof mass “4” are irradiated from the cathode region 42 side. In thismodified diode, the vacancy cluster defects 80 are not formed at the pnjoint interface between the voltage maintaining region 50 and the anoderegion 60 where the electrical field is, in general, the highest in thereverse biased state. Therefore, in this modified diode, the leakcurrent is drastically repressed. Further, the recombination ofelectrons and holes occurs at a more localized area, and the softeningof the recovery current is further improved.

FIG. 15 shows distributions of the impurity density and the crystaldefect density in another modified embodiment. In the diode of themodified embodiment, it is characterized in that the vacancy clusterdefects 80 formed by the irradiation of helium are formed in a narrowrange such that a first group of the vacancy cluster defects 80 a isformed at the anode region 60 side, and a second group of the vacancycluster defects 80 b is formed at the electrical field inhibition region44 side. In this modified diode, since the second group of vacancycluster defects 80 b is formed at a joint interface between theelectrical field inhibition region 44 and the voltage maintaining region50, the recovering time of the recovery current (specifically, that ofits tail current) can be shortened. Further, since the vacancy clusterdefects 80 b have the deep energy level, the shortening effect of therecovering time of recovery current can be maintained even in the hightemperature.

Representative, non-limiting examples of the present invention have beendescribed in further detail with reference to the attached drawings.This detailed description is merely intended to teach a person of skillin the art further details for practicing preferred aspects of thepresent teachings and is not intended to limit the scope of theinvention. Furthermore, each of the additional features and teachingsdisclosed below may be utilized separately or in conjunction with otherfeatures and teachings to provide improved semiconductor devices, aswell as methods for manufacturing the same.

Moreover, combinations of features and steps disclosed in the followingdetail description may not be necessary to practice the invention in thebroadest sense, and are instead taught merely to particularly describerepresentative examples of the invention. Furthermore, various featuresof the above-described and below-described representative examples, aswell as the various independent and dependent claims, may be combined inways that are not specifically and explicitly enumerated in order toprovide additional useful embodiments of the present teachings.

All features disclosed in the description and/or the claims are intendedto be disclosed separately and independently from each other for thepurpose of original written disclosure, as well as for the purpose ofrestricting the claimed subject matter, independent of the compositionsof the features in the embodiments and/or the claims. In addition, allvalue ranges or indications of groups of entities are intended todisclose every possible intermediate value or intermediate entity forthe purpose of original written disclosure, as well as for the purposeof restricting the claimed subject matter.

In one aspect of the present teachings, a semiconductor device maycomprise a semiconductor substrate, a first electrode formed on a firstmain surface of the semiconductor substrate, and a second electrodeformed on a second main surface of the semiconductor substrate. Thesemiconductor substrate may includes a first region in which a densityof oxygen-vacancy defects is more than a density of vacancy clusterdefects, and a second region in which the density of vacancy clusterdefects is greater than the density of oxygen-vacancy defects.

In one aspect of the present teachings, the density of oxygen-vacancydefects may not have a peak in the semiconductor substrate. The term of“the peak” herein means that there is no local maximal value within thesemiconductor substrate along the thickness direction. Therefore, in thecase where the density of oxygen-vacancy defects monotonically increaseor decrease along the thickness direction, it can be read that there isno local maximal value. More preferably, the density of oxygen-vacancydefects may be constant within the semiconductor substrate between thefirst main surface and the second main surface. In these configurations,the increase of leak current is repressed and the reverse recoverycharge (Qrr) is drastically lowered.

In one aspect of the present teachings, the density of oxygen-vacancydefects in the first region is greater than 1×10¹³ cm ³. Theoxygen-vacancy defects having such a high density range can be evaluatedas being purposely formed.

In one aspect of the present teachings, the semiconductor device may bea diode, as mentioned in the above embodiments. In this case, the firstelectrode may be a cathode electrode, and the second electrode may be ananode electrode. It should be noted that, alternatively, the presentteachings is not limited to an embodiment of the diode. For example,IGBT or MOSFET may be realized by the present teaching.

In one aspect of the present teachings, the diode may be a vertical PINdiode which comprises a n⁺-type cathode region, n-type electrical fieldinhibition region, n⁻-type voltage maintaining region and p⁺-type anoderegion.

In one aspect of the present teachings, the first region in which thedensity of oxygen-vacancy defects is greater than the density of vacancycluster defects may be located within the voltage maintaining region.

In one aspect of the present teachings, the density of oxygen-vacancydefects may be at least greater than 1×10¹³ cm ³. The oxygen-vacancydefects having such a density are evaluated as purposely-formed byintroducing oxygen.

In one aspect of the present teachings, the second region in which thedensity of vacancy cluster defects is greater than the density ofoxygen-vacancy defects may be located at a pn joint interface betweenthe voltage maintaining region and the anode region. Further, it ispreferable that the peak value of the second region is located at thevoltage maintaining region side adjacent to the pn joint interfacebetween the voltage maintaining region and the anode region. It is morepreferable that the second region is not located within the anoderegion. In this configuration, additional second region in which thedensity of vacancy cluster defects is greater than the density ofoxygen-vacancy defects may be located at a joint interface between anelectrical field inhibition region and the voltage maintaining region.

In one aspect of the present teachings, the energy level of therecombination center for oxygen-vacancy defects may be an electron traplevel between 0.15 eV to 0.25 eV lower from the conductance band energyedge (Ec).

In one aspect of the present teachings, the energy level of therecombination center for vacancy cluster defects may be an electron traplevel between 0.35 eV to 0.55 eV lower from the conductance band energyedge (Ec).

In one aspect of the present teachings, a manufacturing method of asemiconductor device may be provided. The semiconductor device comprisesa semiconductor substrate including a first region and a second region,wherein a density of oxygen-vacancy defects is greater than a density ofvacancy cluster defects in the first region, and the density of vacancycluster defects is greater than the density of oxygen-vacancy defects inthe second region. The manufacturing method may comprise introducingoxygen into the semiconductor substrate, and irradiating chargedparticles to a predetermined depth in the semiconductor substrate. Thehigh density region of oxygen-vacancy defects is formed within thesemiconductor substrate by performing the step of introducing oxygen.Further, charged particles are irradiated at predetermined depth in thestep of irradiating charged particles. As a result, the first region inwhich the density of oxygen-vacancy defects is greater than the densityof vacancy cluster defects and the second region in which the density ofvacancy cluster defects is greater than the density of oxygen-vacancydefects are formed within the semiconductor substrate.

The step of introducing oxygen may comprise forming an oxide film on anone of main surface of the semiconductor substrate and annealing thesemiconductor substrate in a state that the oxide film is present. Theoxygen can be introduced within the semiconductor substrate by using thesimple process.

In the step of forming the oxide film, an oxidation temperature may beset between 1100-1200 degrees Celsius, and an oxidation time may be setbetween 10-500 minutes. In the step of annealing the semiconductorsubstrate, annealing temperature may be set higher than 1150 degreesCelsius. As a result, a high density of oxygen can be introduced withinthe semiconductor substrate.

In the step of introducing oxygen, an oxygen density within thesemiconductor substrate may rise at an entire area along a thicknessdirection. As a result, the high density region of oxygen-vacancydefects is surely formed within the semiconductor substrate.

1.-5. (canceled)
 6. A manufacturing method of a semiconductor devicecomprising a semiconductor substrate including a first region and asecond region, wherein a density of oxygen-vacancy defects is greaterthan a density of vacancy cluster defects in the first region, and thedensity of vacancy cluster defects is greater than the density ofoxygen-vacancy defects in the second region, the method comprising:introducing oxygen into the semiconductor substrate; and irradiatingcharged particles to a predetermined depth in the semiconductorsubstrate
 7. The manufacturing method according to claim 6, wherein saidintroducing oxygen comprising: forming an oxide film on one of mainsurfaces of the semiconductor substrate; and annealing the semiconductorsubstrate in a state that the oxide film is present.
 8. Themanufacturing method according to claim 7, wherein in said forming theoxide film, an oxidation temperature is set between 1100-1200 degreesCelsius, and an oxidation time is set between 10-500 minutes, and insaid annealing the semiconductor substrate, an annealing temperature isset highter than 1150 degrees Celsius.
 9. The manufacturing methodaccording to claim 6, wherein in said introducing oxygen, an oxygendensity within the semiconductor substrate rises at an entire area alonga thickness direction.